Leaf Springs Vs. Everything Else

[High Plains Mopars]

Yes, Tony is correct. The name in the signature is something we started here a year or two ago.

I'd suggest checking out the rule book in greater detail to understand where you will fall. The tubular arms and braces may already put you up a class or two. SCCA has only recently allowed the use of sub-frame connectors and those have to be bolt in units. So, if you want to really be competitive in a specific class, you need to define the build by the mods allowed by the rule book. If you only want to compete with yourself on timed improvements or run Goodguys or attend some of the pro touring events listed on this site, then you can build it however you want.

[Fras]

If you were a little closer to Indy I would be happy to take you for a spin in my 550hp 600tq 77 t/a with the ptfb comp kit. I've been autocrossing it recently and I've been very happy. If you've got any questions feel free to pm me.

Is this a leaf spring kit?

[Z06killinSBF]

I sure hope leaf springs are good. I've been putting in effort to make mine work on a tubed set up!!

[John Wright]

Another thing to mention, the rate of the leafs are progressive and coils are more linear.
Leafs can wrap in both directions...hard launch off the corner and during braking, and can be upsetting at the rear tires if they rapidly unload/load/unload.

[exwestracer]

On a performance or racing chassis, we expend a lot of effort getting the compliance out of all the suspension linkage (reinforcement, heim joints, etc.). The leaf spring is by definition compliant, as it needs to be a spring AND linkage at the same time. Sure, you can make a leaf spring car handle really well. Does it make as much sense to start there as opposed to a linkage and coil system? No.

[cornfedbill]

A panhard bar is good. A watts link is better. However, leaf springs have their own roll center. To add a second locating device that forces the car to roll about a different center can create binding and an undesired stiff roll rate in the rear.

If I were to use a watts link, I would make an effort to align the roll centers of the leafs with the watts link. My current plan is to run without a secondary locating device.

Cal-tracs are great for drag racing. I have a friend who runs low 10's in a street driven LS powered Colorado pick-up that will carry the front wheels that runs only leafs and Cal-tracs.

However, I am not sure of their affect on cornering when exiting under hard acceleration. Does anyone here run Cal-tracs for autocross? I am very interested to know their results. I have toyed with the idea of adding them to my Nova, but am not sure it is the best set-up for me. I am only running about 425 lb-ft of torque with 225 lb/in Landrum leafs with the Hotchkis Swivel Max upgrade. I don't think spring wrap will be my biggest problem. I could be wrong.

I do believe that leaf springs are a good alternative for those of us on a limited budget. There is a lot of data on them from the days of Trans Am racing when leaf springs were required. **** Guldstrand and Herb Adams worked wonders with leaf spring cars.

[TheBandit]

No, I'm not missing that point. That is why I said it can be a very forgiving suspension design. While the leaf does do all those things, it doesn't diminish its role as a spring nor make it any less of a performer for the average guy. Yes, a coil set up allows individual components to be added to perform specific tasks, and potentially allow more defined adjustment in those roles, whereas a leaf spring set up has to perform all those same functions and cannot be as easily designed to accomodate simple or easy changes. I'd also say if you understand the traction circle concept, you know that any tire will only generate X amount of grip. That grip can be accellerating, braking, turning, or any combination of those. The loads a tire sees under braking or accellerating are X-Y. The loads felt during cornering are X-Z. The combination of turning and either accelerating or braking is X-Y-Z. Simple as that. Regardless of what device is doing what in the suspension, when those loads are applied or transfered, the tires will feel those formulas and will only generate as much grip as it is designed to. The spring design applying that force in your average street car is less important than the amount of that force and rate at which its applied. If you stab throttle and crank the steering, you're going to overload a coil as quickly as you overload a leaf. If you have too much rate going in to a corner, you will overload a coil as quickly as a leaf.

First, let me apologize for using the term "missing the point". I think that was inflammatory and that's now how I meant it; I only meant to add information to the already good information you provided.



Yes a spring is a spring and spring rate is spring rate, however the geometry/kinematics of the suspension dictate kinematic properties which will determine how the tires are loaded. I'll take roll stiffness as an example. Depending on where the roll center is located, a given spring rate at either side of the axle will result in a different roll stiffness. Even if the rates of a coil and a leaf are the same, if the roll center is different, the roll stiffness will be different. This affects the ratio of roll stiffness front to rear, which will determine how loads are transferred when cornering. For example, if the front has a higher roll stiffness than the rear, more load will be applied to front outside tire in a corner. You will operate in a different part of the traction circle for each tire because the applied loads are different. This is just one example that I am aware of. There are other suspension properties like antisquat which are much more constrained with a leaf spring design than a link suspension.

[High Plains Mopars]

Sure, you can make a leaf spring car handle really well. Does it make as much sense to start there as opposed to a linkage and coil system? No.

Agreed and I'd add that if you have to significantly re-engineer the leaf spring layout to make it work for your application, then it may be better to start with a link set up. For most of us using these vehicles as predominately street cars, an aftermarket leaf layout can be a much simpler and more economicly friendly approach to get our butts in the seat and the car out of the garage.

A panhard bar is good. A watts link is better. However, leaf springs have their own roll center. To add a second locating device that forces the car to roll about a different center can create binding and an undesired stiff roll rate in the rear.

That can be an issue which is why you need to replace the front spring eyes with a pivot device and put soft durometer bushings in the shackles. This reduces the springs ability to act as a roll resistant device and instead puts that function on the lateral locating device. Failure to allow the springs to pivot will produce binding as the basic flat design of a leaf naturally resist twisting produced by body roll. Similarly, a watts is a better locating device, but its physical layout in relationship to other items in the area - axle housing, tanks, exhaust, etc, may result in compromised layouts that do not allow it to work as effectively as a panhard. Every chassis is different so review carefully. FWIW, the '70 AAR Cudas ran panhards, the Dodge Challenger TAs ran watts. The Cudas outqualified the Challengers early in the season until the Dodges swapped over to Panhards. Granted, development time on those chassis was limited and a one year only deal, so perhaps in time they could have made the watts work better. However, sometimes the better theory doesn't always produce the best results in the middle of the battle.

First, let me apologize for using the term "missing the point". I think that was inflammatory and that's now how I meant it; I only meant to add information to the already good information you provided.

Clint, thanks and likewise. Actually, after reading your post above, I believe you and I agree on our points even if appears we don't. I will say that leaf spring design layouts can be quite restraining and depending on the effort the OEM put into that design, can be a decent starting point or a real pain in the butt to work around.

I'd certainly recommend reading Afco's analysis of leaf spring layouts to any of the thread followers in here so they can better understand some of the dynamics of a leaf set up. It is not the end all of leaf design, but it does hit some key points. http://www.afcoracing.com/tech_pages/leaf.shtml

[TheBandit]

No hard feelings at all Tony. I need to choose my words better because I think I come across as very arrogant at times. Maybe I am arrogant - feel free to put me in my place!

A panhard bar is good. A watts link is better. However, leaf springs have their own roll center. To add a second locating device that forces the car to roll about a different center can create binding and an undesired stiff roll rate in the rear.

If I were to use a watts link, I would make an effort to align the roll centers of the leafs with the watts link. My current plan is to run without a secondary locating device.

I would like to hear a bit more on this subject. You can find some discussion here: https://www.pro-touring.com/showthread.php?89108

[cornfedbill]

Clint,

I think Tony did a very good job explaining what I was trying to say about panhard bars and watts links with leaf springs.

If one were able to take the time to alter the mounting points and the arc of the leaf springs, use a good spherical bearing in the front eye and a very loose rear bushing, a watts link may be the hot setup. But then, that is a lot of work and can be costly.

As you know Mary Pozzi ran real fast with rear leaf springs and no locating device for a long time. Granted, she would run fast in anything. But the point is that leaf springs are not going to prevent a good driver from running fast.

I am real excited to get my Hotchkis front bearings into my springs. I will run their Delrin rear bushings and stiff shackles because I am not ready to add a panhard bar or watts link. I have contemplated using sliders, but am concerned about their durability on the street on a daily driver. I worry that they may deteriorate or begin to bind on the street if I don't take time to maintain them like a racer would.

I think the biggest drawback on my leaf spring setup will be weight. I think I could design and build a much lighter three link with a watts link and coilovers. I just want my Nova build to look very stock to keep it subtle. I have a '55 Bel Air that I want to convert to a 3 or 4 link. That project is not destined to look stock.

[Rotary]

I think this thread has changed my mind on suspension a bit. I was hard set on saving up for a nice multi link set up. I still will get there eventually but for my purposes and driving level i think spending 700 instead of 3-5k might be the better way to go for now. Sure i'll eventually get the high end set up, but for now maybe a good leaf set up will allow me to invest in other areas of the car, and still allow the car to be somewhat dialed in at the autocross.

[tflyboy77]

If you were a little closer to Indy I would be happy to take you for a spin in my 550hp 600tq 77 t/a with the ptfb comp kit. I've been autocrossing it recently and I've been very happy. If you've got any questions feel free to pm me.

Is this a leaf spring kit?

Yes it is. This I ordered this kit with spherical front spring eyes which helps out a ton. They just put spherical bearings in instead of the front bushings.

[GATA79]

Does Dave put them in for ya? I think I'm going to end up running his kit in all honesty.

[SR71]

parallel leaf springs can be made to work well. BUT by the time you buy leafs, watts link and caltrac type bars, you are closing in on the price of a ridetech 4-link kit. and if you are going to buy a nice set of adjustable shocks, coilovers are little more that stock type shocks.

leafs are not as good as link type suspensions. how far behind they are is open for debate. case and point....how many modern performance cars do you see with factory parallel leaf springs? there is a reason for that. sure Mary's car worked great with the leaf set-up. but I think I recall David talking about how harsh the ride was and Mary saying he was just a wuss.

I don't settle well. I am much better off getting what I want the first time. it saves me money in the long run. if you really want a link type suspension, don't try to convince yourself that leafs are just as good all around....because they aren't. making them work in one area will cost you in the other.

[Rod]

Leaf Springs Vs. Everything Else

awesome, subject.... I will say that a leaf spring setup is very fast on the autocross or track easy to set up some good spherical bearings in the front of the leaf, nice adjustable rear sway bar and shocks, and your good to go, at larger events (more time) I also use the lowering blocks also on the car to create additional oversteer, with a 1inch block the car is has almost a neutral attitude, with a 1.5 inch block and I have a little push, simple, a bunch of my friends are running the newer multi-link suspensions, there also very nice setups, what I have noticed is that there two completely different driving styles, and require some different lines around the track, but they accomplish the same thing, it really comes down to what you like

[tflyboy77]

Does Dave put them in for ya? I think I'm going to end up running his kit in all honesty.

Ya, he installs them before they ship. I'll get back to you guys on your pm's I've just been busy at work.

[cornfedbill]

Tom, you are correct that link type suspensions are ultimately better. However, after working more than 20 years in the auto industry in Detroit, I found that marketing drove technology more than performance. New cars with 4 wheel independent suspensions and multi-cam engines were driven more by marketing than performance many times.

The Gen 5 Camaros are great cars, but carry a lot of weight due to the independent rear end design - a decision driven by marketing, not ultimate performance. If performance were the goal, the car would have a lighter IRS or a multi-link live axle.

I still stand by my opinion that for most budget-minded builds, a good leaf spring set-up is sufficient. Once one goes to the cost of adding Caltracs and a Watts link, the cost advantage diminishes.

I do agree with you that when the final goal is a multi-link, one would be wise to go there first rather than to spend money upgrading a leaf spring rear end only to replace it later and discard the upgrades.

This is a very interesting discussion. It has made me review my decisions for my rear suspension. I will still go with the rear leafs without a panhard bar or Watts link. But it did help me to review my rationale and to check my logic.

[High Plains Mopars]

parallel leaf springs can be made to work well. BUT by the time you buy leafs, watts link and caltrac type bars, you are closing in on the price of a ridetech 4-link kit. and if you are going to buy a nice set of adjustable shocks, coilovers are little more that stock type shocks.

leafs are not as good as link type suspensions. how far behind they are is open for debate. case and point....how many modern performance cars do you see with factory parallel leaf springs? there is a reason for that. sure Mary's car worked great with the leaf set-up. but I think I recall David talking about how harsh the ride was and Mary saying he was just a wuss.

I'd say the total cost involved depends on what you do with them. Sure, if you put new composite leafs, a watts set up, cal-tracs, adjustable sway bars, and high end shocks, you will be close to a basic link kit. However, the thing is you don't necessarily need to go that far with a leaf set up. A Hotchkis kit with geometery correct multi-leafs, adjustable rear bar, and RCD Bilsteins is only going to run $800-900, can be bolted in on Saturday afternoon, and have you turning laps Sunday morning without any cutting or welding.

I don't think the modern car reference is germain either. No new cars are available with carburators, yet a carb can still produce as much power as an EFI. Sometimes I think the whole "new car" point of view on things is what drives a lot of the perception that if it is an old design, its worthless. In reality, it may not cost as much to update the older stuff compared to re-engeering a whole new fit up of modern components. As Bandit and I were going around about, a spring is a spring, is a spring. Its only the supporting hardware such as links, that allow geater adjustability over leafs, but that also means they have greater opportunity for errors if you're unsure how and why changes are needed.

Leaf Springs Vs. Everything Else

awesome, subject.... I will say that a leaf spring setup is very fast on the autocross or track easy to set up some good spherical bearings in the front of the leaf, nice adjustable rear sway bar and shocks, and your good to go, at larger events (more time) I also use the lowering blocks also on the car to create additional oversteer, with a 1inch block the car is has almost a neutral attitude, with a 1.5 inch block and I have a little push, simple, a bunch of my friends are running the newer multi-link suspensions, there also very nice setups, what I have noticed is that there two completely different driving styles, and require some different lines around the track, but they accomplish the same thing, it really comes down to what you like

This sounds like a relevent, real world experience that shows it doesn't take a whole lot of work get leafs working well and there is some minimal adjustability in fairly basic set up. I'll also chime in and say in my oval track days, the class I was in required the OEM set up, which allowed leafs or coils. Fastest lap of the day could be either and the coil cars did not have a lock on the best times. Granted, as you moved up classes the coil overs became the dominate choice because of the adjustability and light weight. But, I think that highlights something a lot of guys overlook when they build a car...if the combo is capable if supporting the skill level of 90% of the drivers out there, why do you need to build a system capable of supporting the skill set of the 97th percentile? Particularly if your skills are in that bottom 90% range or lower. While we'd all like to think we are awesome drivers, the reality is not all of us are. I'd also say that unless you are running in a class that needs rapid spring rate changes of as little as 50# and a link pivot adjustment will give you that extra .01 advantage, links and coil overs are almost a waste on a street car where owners set em and forget em.

[regal454]

...if the combo is capable if supporting the skill level of 90% of the drivers out there, why do you need to build a system capable of supporting the skill set of the 97th percentile? Particularly if your skills are in that lower 90% range or lower.

Great Point^^^ Plus it's a LOT cooler to beat other cars that have spent thousands of dollars more on their suspensions than you have. Mary Pozzi has done that for years!

[cornfedbill]

I don't think the modern car reference is germain either. No new cars are available with carburators, yet a carb can still produce as much power as an EFI. Sometimes I think the whole "new car" point of view on things is what drives a lot of the perception that if it is an old design, its worthless.

My point exactly.

... I think that highlights something a lot of guys overlook when they build a car...if the combo is capable if supporting the skill level of 90% of the drivers out there, why do you need to build a system capable of supporting the skill set of the 97th percentile? Particularly if your skills are in that lower 90% range or lower.

Very well stated. I think we all want to "keep up with the Jones'" sometimes and overlook what is best for us.

Build what makes sense for your build at this time. Save your money for gas and tires!